Control channel signaling techniques in wireless systems with multiple possible transmission time intervals

ABSTRACT

Control information may be transmitted for different TTI lengths. Different control information for the different TTIs may be transmitted using control channel resources that are established for communication of control information, such as a physical downlink control channel (PDCCH), for example. Control information for a first TTI may be located in a first set of resources, and control information for a second TTI may be located in a second set of resources. The first set of resources may be located within a first search space that may be searched by a user equipment (UE) to identify the first control information. The second set of resources may be located within a second search space that may be searched by the UE to identify the second control information.

CROSS REFERENCES

The present Application for Patent claims priority to U.S. ProvisionalPatent Application No. 62/290,899 entitled “CONTROL CHANNEL SIGNALINGTECHNIQUES IN WIRELESS SYSTEMS WITH MULTIPLE POSSIBLE TRANSMISSION TIMEINTERVALS,” filed Feb. 3, 2016, assigned to the assignee hereof.

BACKGROUND

The following relates generally to wireless communication, and morespecifically to control channel signaling for systems configured to usemultiple possible transmission time interval (TTI) lengths.

Wireless communications systems are widely deployed to provide varioustypes of communication content such as voice, video, packet data,messaging, broadcast, and so on. These systems may be capable ofsupporting communication with multiple users by sharing the availablesystem resources (e.g., time, frequency, and power). Examples of suchmultiple-access systems include code division multiple access (CDMA)systems, time division multiple access (TDMA) systems, frequencydivision multiple access (FDMA) systems, and orthogonal frequencydivision multiple access (OFDMA) systems. A wireless multiple-accesscommunications system may include a number of base stations, eachsimultaneously supporting communication for multiple communicationdevices, which may be otherwise known as user equipment (UE).

Wireless multiple-access technologies have been adopted in varioustelecommunication standards to provide a common protocol that enablesdifferent wireless devices to communicate on a municipal, national,regional, and even global level. A wireless multiple-accesscommunications system, including a system operating according to theLong Term Evolution (LTE) standard, may include a number of basestations, each simultaneously supporting communication for multiple UEs.Uplink control information (UCI) and downlink control information (DCI)may be exchanged between a UE and a base station. UCI and DCI mayinclude data such as acknowledgement data, channel state information(CSI), scheduling information (e.g., assignment information, modulationand coding scheme (MCS)), or the like. UCI may be transmitted from a UEto a base station using a Physical Uplink Control Channel (PUCCH) or aPhysical Uplink Shared Channel (PUSCH), while DCI may be transmittedfrom a base station to a UE using a Physical Downlink Control Channel(PDCCH) or a Physical Downlink Shared Channel (PDSCH), for example.

In some applications, latency for various UEs may be reduced byselecting a TTI and adapting uplink and downlink resources allocated fortransmitting control information (e.g., UCI, DCI) based on data traffic.Multiple different TTIs may in some cases result in different controlinformation that is associated with each TTI, and efficient transmissionof such control information may enhance the overall efficiency ofsystems that use multiple different TTIs.

SUMMARY

The described techniques relate to improved methods, systems, devices,or apparatuses that support control channel signaling in systemsconfigurable to use multiple transmission time interval (TTI) lengths.The described techniques may provide for control informationtransmission for different TTI lengths, such as certain transmissionsthat use a 1 millisecond (ms) (or legacy) TTI along with a shorter TTIsuch as a 0.5 ms (or slot) TTI. Different control information for thedifferent TTIs may be transmitted using control channel resources thatare established for communication of control information, such as aphysical downlink control channel (PDCCH), for example. Differentresources within the control channel may be configured to providecontrol information for the different TTI transmissions. In someexamples, control information for a 1 ms TTI may be located in a firstset of resources, and control information for a 0.5 ms TTI may belocated in a second set of resources.

In some examples, the first set of resources may be located within afirst search space that may be searched by a user equipment (UE) toidentify the 1 ms control information. The second set of resources maybe located within a second search space that may be searched by the UEto identify the 0.5 ms control information. In some examples, the secondsearch space may be determined based on the first search space, such asthrough being a subset of the first search space or otherwise derivedbased on the first search space. In some examples, blind decoding of thefirst or second search spaces to determine the control information maybe based on a limited set of decoding candidates, DCI sizes, or based ona configured hybrid automatic repeat request (HARD) round trip time(RTT).

A method of wireless communication is described. The method may includeidentifying a first transmission time interval (TTI) with a firstduration that includes two or more symbol periods and a second TTI witha second duration that is less than the first duration, identifying afirst search space for monitoring for first control informationassociated with the first TTI, determining, based at least in part onthe first search space, a second search space for monitoring for secondcontrol information associated with the second TTI, and monitoring atleast one of the first search space for the first control information orthe second for the second control information.

An apparatus for wireless communication is described. The apparatus mayinclude means for identifying a first TTI with a first duration thatincludes two or more symbol periods and a second TTI with a secondduration that is less than the first duration, means for identifying afirst search space for monitoring for first control informationassociated with the first TTI, means for determining, based at least inpart on the first search space, a second search space for monitoring forsecond control information associated with the second TTI, and means formonitoring at least one of the first search space for the first controlinformation or the second for the second control information.

A further apparatus is described. The apparatus may include a processor,memory in electronic communication with the processor, and instructionsstored in the memory. The instructions may be operable to cause theprocessor to identify a first TTI with a first duration that includestwo or more symbol periods and a second TTI with a second duration thatis less than the first duration, identify a first search space formonitoring for first control information associated with the first TTI,determine, based at least in part on the first search space, a secondsearch space for monitoring for second control information associatedwith the second TTI, and monitor at least one of the first search spacefor the first control information or the second for the second controlinformation.

A non-transitory computer readable medium for wireless communication isdescribed. The non-transitory computer-readable medium may includeinstructions to cause a processor to identify a first TTI with a firstduration that includes two or more symbol periods and a second TTI witha second duration that is less than the first duration, identify a firstsearch space for monitoring for first control information associatedwith the first TTI, determine, based at least in part on the firstsearch space, a second search space for monitoring for second controlinformation associated with the second TTI, and monitor at least one ofthe first search space for the first control information or the secondfor the second control information.

In some examples of the method, apparatus, or non-transitorycomputer-readable medium described above, the second search space iscorrelated to the first search space. In some examples of the method,apparatus, or non-transitory computer-readable medium described above,the second search space is a subset of the first search space.

In some examples of the method, apparatus, or non-transitorycomputer-readable medium described above, the identifying the firstsearch space comprises: deriving a set of decoding candidates fordecoding of received wireless transmissions and identification (ID) ofthe first control information and the second control information. Someexamples of the method, apparatus, or non-transitory computer-readablemedium described above may further include processes, features, means,or instructions for identifying a first subset of the decodingcandidates as being in the first search space.

In some examples of the method, apparatus, or non-transitorycomputer-readable medium described above, the determining the secondsearch space comprises: identifying a second subset of the decodingcandidates as being in the second search space. In some examples of themethod, apparatus, or non-transitory computer-readable medium describedabove, the first subset of decoding candidates and the second subset ofdecoding candidates are non-overlapping subsets of the set of decodingcandidates.

In some examples of the method, apparatus, or non-transitorycomputer-readable medium described above, the deriving is based on oneor more of a UE network identifier, a random seed, or a total sizeavailable for control information. In some examples of the method,apparatus, or non-transitory computer-readable medium described above,the determining the second search space comprises: deriving the secondsearch space based on one or more of a second UE network identifier or asecond random seed.

In some examples of the method, apparatus, or non-transitorycomputer-readable medium described above, the first control informationcomprises first downlink control information (DCI) having a first DCIsize and a first DCI format, and the second control informationcomprises second DCI having a second DCI size and a second DCI format,and where one or more of the first DCI size and the second DCI size orthe first DCI format and the second DCI format is different.

In some examples of the method, apparatus, or non-transitorycomputer-readable medium described above, the first DCI size is largerthan the second DCI size. In some examples of the method, apparatus, ornon-transitory computer-readable medium described above, the first DCIsize and second DCI size are the same, and where one or more bits of thesecond DCI provide different information than corresponding bits in thefirst DCI.

In some examples of the method, apparatus, or non-transitorycomputer-readable medium described above, the first DCI includes a firstnumber of cyclic redundancy check (CRC) bits, and the second DCIincludes a second number of CRC bits that is greater than the firstnumber of CRC bits.

Some examples of the method, apparatus, or non-transitorycomputer-readable medium described above, the monitoring may includeblind decoding wireless transmissions received in the first search spacefor the first control information. Some examples of the method,apparatus, or non-transitory computer-readable medium described abovemay further include processes, features, means, or instructions forblind decoding wireless transmissions received in the second searchspace for the second control information.

Some examples of the method, apparatus, or non-transitorycomputer-readable medium described above may further include processes,features, means, or instructions for identifying a set of blind decodingcandidates for blind decoding transmissions received in the secondsearch space based on one or more of an available number of aggregationlevels for second TTI transmissions or an available DCI format for thesecond control information.

In some examples of the method, apparatus, or non-transitorycomputer-readable medium described above, a different set of blinddecoding candidates for the first search space is identified whentransmissions using the second TTI are configured than whentransmissions using the second TTI are not configured.

Some examples of the method, apparatus, or non-transitorycomputer-readable medium described above may further include processes,features, means, or instructions for identifying a set of blind decodingcandidates for blind decoding transmissions received in the secondsearch space based on a round trip time (RTT) for hybrid automaticrepeat request (HARD) feedback associated with the second controlinformation.

Some examples of the method, apparatus, or non-transitorycomputer-readable medium described above may further include processes,features, means, or instructions for identifying a first RTT for HARQfeedback associated with the first control information. Some examples ofthe method, apparatus, or non-transitory computer-readable mediumdescribed above may further include processes, features, means, orinstructions for identifying a second RTT for HARQ feedback associatedwith the second control information, where the second RTT is shorterthan the first RTT.

In some examples of the method, apparatus, or non-transitorycomputer-readable medium described above, the second RTT is determinedbased on a capability of a UE receiving the second control information.In some examples of the method, apparatus, or non-transitorycomputer-readable medium described above, the first RTT is determined tobe a legacy RTT or a shorter RTT than the legacy RTT based on acapability of the UE.

In some examples of the method, apparatus, or non-transitorycomputer-readable medium described above, the second control informationcomprises a first subset of second control information transmitted in afirst slot of a wireless transmission subframe and a second subset ofsecond control information transmitted in a second slot of the wirelesstransmission subframe.

In some examples of the method, apparatus, or non-transitorycomputer-readable medium described above, the first subset transmittedin the first slot of the wireless transmission subframe is transmittedin a control channel that is time division multiplexed with sharedchannel data transmissions in the first slot, and wherein second subsettransmitted in the second slot of the wireless transmission subframe istransmitted in a second control channel that is both time divisionmultiplexed and frequency division multiplexed with shared channel datatransmissions in the second slot.

Some examples of the method, apparatus, or non-transitorycomputer-readable medium described above may further include processes,features, means, or instructions for determining a starting symbol forthe shared channel data transmissions in the second slot based on one ormore of a configured starting symbol location or a symbol location ofthe second subset of second control information.

Some examples of the method, apparatus, or non-transitorycomputer-readable medium described above may further include processes,features, means, or instructions for determining a third search space inthe second slot for monitoring for the second subset of second controlinformation. Some examples of the method, apparatus, or non-transitorycomputer-readable medium described above may further include processes,features, means, or instructions for determining a starting symbol forthe shared channel data transmissions in the second slot based on thethird search space.

In some examples of the method, apparatus, or non-transitorycomputer-readable medium described above, the third search space isdetermined based on a set of resource blocks (RBs) of the second slotconfigured for control information transmissions. In some examples ofthe method, apparatus, or non-transitory computer-readable mediumdescribed above, the first search space and second search space aredistributed over a system bandwidth for transmissions in the first slot,and where the third search space is distributed over a subset of thesystem bandwidth.

In some examples of the method, apparatus, or non-transitorycomputer-readable medium described above, the third search space isdetermined based on a transmission mode associated with the secondcontrol information.

In some examples of the method, apparatus, or non-transitorycomputer-readable medium described above, the second subset of secondcontrol information comprises one or more of physical downlink controlchannel (PDCCH) information or physical control format indicator channel(PCFICH) information transmitted in a second slot of the wirelesstransmission subframe.

The foregoing has outlined rather broadly the features and technicaladvantages of examples according to the disclosure in order that thedetailed description that follows may be better understood. Additionalfeatures and advantages will be described hereinafter. The conceptionand specific examples disclosed may be readily utilized as a basis formodifying or designing other structures for carrying out the samepurposes of the present disclosure. Such equivalent constructions do notdepart from the scope of the appended claims. Characteristics of theconcepts disclosed herein, both their organization and method ofoperation, together with associated advantages will be better understoodfrom the following description when considered in connection with theaccompanying figures. Each of the figures is provided for the purpose ofillustration and description only, and not as a definition of the limitsof the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

A further understanding of the nature and advantages of the presentinvention may be realized by reference to the following drawings. In theappended figures, similar components or functions may have the samereference label. Further, various components of the same type may bedistinguished by following the reference label by a dash and a secondlabel that distinguishes among the similar components. If just the firstreference label is used in the specification, the description isapplicable to any one of the similar components having the same firstreference label irrespective of the second reference label.

FIG. 1 illustrates an example of a wireless communications system thatsupports control channel signaling with multiple TTI lengths inaccordance with aspects of the present disclosure;

FIG. 2 illustrates an example of a wireless communications system thatsupports control channel signaling with multiple TTI lengths inaccordance with aspects of the present disclosure;

FIG. 3 illustrates an example of a wireless subframe that supportscontrol channel signaling with multiple TTI lengths in accordance withaspects of the present disclosure;

FIG. 4 illustrates another example of a wireless subframe that supportscontrol channel signaling with multiple TTI lengths in accordance withaspects of the present disclosure;

FIG. 5 illustrates an example of uplink and downlink communications thatsupport control channel signaling with multiple TTI lengths inaccordance with aspects of the present disclosure;

FIG. 6 illustrates another example of uplink and downlink communicationsthat support control channel signaling with multiple TTI lengths inaccordance with aspects of the present disclosure;

FIG. 7 illustrates another example of uplink and downlink communicationsthat support control channel signaling with multiple TTI lengths inaccordance with aspects of the present disclosure;

FIG. 8 illustrates another example of uplink and downlink communicationsthat support control channel signaling with multiple TTI lengths inaccordance with aspects of the present disclosure;

FIG. 9 illustrates an example of a wireless subframe that supportscontrol channel signaling with multiple TTI lengths in accordance withaspects of the present disclosure;

FIG. 10 illustrates an example of a process flow in a system thatsupports control channel signaling with multiple TTI lengths inaccordance with aspects of the present disclosure;

FIGS. 11 through 13 show block diagrams of a wireless device thatsupports control channel signaling with multiple TTI lengths inaccordance with aspects of the present disclosure;

FIG. 14 illustrates a block diagram of a system including a UE thatsupports control channel signaling with multiple TTI lengths inaccordance with aspects of the present disclosure; and

FIGS. 15 through 19 illustrate methods for control channel signalingwith multiple TTI lengths in accordance with aspects of the presentdisclosure.

DETAILED DESCRIPTION

Certain wireless communication applications may be bursty in nature. Aparticular user equipment (UE) may, for example, operate a relativelylong period without sending or receiving data, and then a relativelylarge amount, or burst, of data may queue up for transmission to the UE.The data may be associated with a latency sensitive application, such asa vehicle communication system, a gaming application, or otherimplementation that is delay intolerant. A base station may, in someexamples, configure multiple different transmission time intervals(TTIs) for communications with a UE. In some examples, a wirelesssubframe may be a 1 ms subframe and contain two slots that are each 0.5ms. Some examples provide for control information transmission for 1 ms(of legacy) TTI lengths along with different control information for the0.5 ms (or slot) TTIs. The control information may be transmitted usingcontrol channel resources that are established for communication ofcontrol information, such as a physical downlink control channel (PDCCH)or enhanced PDCCH (ePDCCH), for example. Different resources within thecontrol channel may be configured to provide control information for thedifferent TTI transmissions.

In some examples, control information for a 1 ms TTI may be located in afirst set of resources, and control information for a 0.5 ms TTI may belocated in a second set of resources. In some examples, the first set ofresources may be located within a first search space that may besearched by a user equipment (UE) to identify the 1 ms controlinformation. The second set of resources may be located within a secondsearch space that may be searched by the UE to identify the 0.5 mscontrol information. In some examples, the second search space may bedetermined based on the first search space, such as through being asubset of the first search space or otherwise derived based on the firstsearch space. In some examples, blind decoding of the first or secondsearch spaces to determine the control information may be based on alimited set of decoding candidates, DCI sizes, or based on a configuredhybrid automatic repeat request (HARQ) round trip time (RTT).

As described herein, available resources and parameters forcommunication of control information using low latency TTIs may bedetermined with respect to resources of other, longer duration TTIs. Asystem may configure low latency TTIs to support concurrent operationwith longer duration TTIs. For instance, resource availability for lowlatency data transmissions may be symbol dependent. Whether a symbol oflonger duration TTI includes a secondary synchronization signal (SSS) orphysical broadcast channel (PBCH) information may affect resourceavailability for a low latency TTI control information, and resourceswith PBCH information or a SSS may be omitted from the search space.

Aspects of the disclosure introduced above are described below in thecontext of a wireless communication system. A wireless communicationsystem may include a base station and a UE which are both configurableto communication using one or more of multiple TTI durations asdescribed herein. Aspects of the disclosure are further illustrated byand described with reference to apparatus diagrams, system diagrams, andflowcharts that relate to control channel signaling with multiple TTIlengths.

FIG. 1 illustrates an example of a wireless communications system 100 inaccordance with various aspects of the present disclosure. The wirelesscommunications system 100 includes base stations 105, UEs 115, and acore network 130. In some examples, the wireless communications system100 may be a Long Term Evolution (LTE)/LTE-Advanced (LTE-A) network. Thewireless communications system 100 may support low latency applicationsand communications with multiple TTI lengths as described herein.Additionally, the wireless communications system 100 may multiple HARQRTTs for low latency applications and multiple TTI length operations.

Base stations 105 may wirelessly communicate with UEs 115 via one ormore base station antennas. Each base station 105 may providecommunication coverage for a respective geographic coverage area 110.Communication links 125 shown in wireless communications system 100 mayinclude uplink transmissions from a UE 115 to a base station 105, ordownlink transmissions, from a base station 105 to a UE 115. UEs 115 maybe dispersed throughout the wireless communications system 100, and eachUE 115 may be stationary or mobile. A UE 115 may also be referred to asa mobile station, a subscriber station, a remote unit, a wirelessdevice, an access terminal (AT), a handset, a user agent, a client, orlike terminology. A UE 115 may also be a cellular phone, a wirelessmodem, a handheld device, a personal computer, a tablet, a personalelectronic device, a machine type communication (MTC) device, etc.

Base stations 105 may communicate with the core network 130 and with oneanother. For example, base stations 105 may interface with the corenetwork 130 through backhaul links 132 (e.g., S1). Base stations 105 maycommunicate with one another over backhaul links 134 (e.g., X2) eitherdirectly or indirectly (e.g., through core network 130). Base stations105 may perform radio configuration and scheduling for communicationwith UEs 115, or may operate under the control of a base stationcontroller (not shown). In some examples, base stations 105 may be macrocells, small cells, hot spots, or the like. Base stations 105 may alsobe referred to as eNodeBs (eNBs) 105.

Data communications within wireless communications system 100 may bedivided into and described with reference to logical channels, transportchannels, and physical (PHY) layer channels. Channels may also beclassified into Control Channels and Traffic Channels. Logical controlchannels may include paging control channel (PCCH) for paginginformation, broadcast control channel (BCCH) for broadcast systemcontrol information, multicast control channel (MCCH) for transmittingmultimedia broadcast multicast service (MBMS) scheduling and controlinformation, dedicated control channel (DCCH) for transmitting dedicatedcontrol information, common control channel (CCCH) for random accessinformation, dedicated traffic channel (DTCH) for dedicated UE data, andmulticast traffic channel (MTCH), for multicast data.

DL transport channels may include broadcast channel (BCH) for broadcastinformation, a downlink shared channel (DL-SCH) for data transfer,paging channel (PCH) for paging information, and multicast channel (MCH)for multicast transmissions. UL transport channels may include randomaccess channel (RACH) for access and uplink shared channel (UL-SCH) fordata.

DL PHY channels may include physical broadcast channel (PBCH) forbroadcast information, physical control format indicator channel(PCFICH) for control format information, physical downlink controlchannel (PDCCH) for control and scheduling information, physical HARQindicator channel (PHICH) for HARQ status messages, physical downlinkshared channel (PDSCH) for user data and physical multicast channel(PMCH) for multicast data. UL PHY channels may include physical randomaccess channel (PRACH) for access messages, physical uplink controlchannel (PUCCH) for control data, and physical uplink shared channel(PUSCH) for user data.

PDCCH carries downlink control information (DCI) which, in legacyoperations in included in at least one control channel element CCE,which may consist of nine logically contiguous resource element groups(REGs), where each REG contains 4 REs. In some examples of the currentdisclosure, the format of the DCI may be different for 1 ms TTIs thanfor slot TTIs, as will be discussed herein. DCI includes informationregarding DL scheduling assignments, UL resource grants, transmissionscheme, UL power control, hybrid automatic repeat request (HARQ)information, MCS and other information. The size and format of the DCImessages can differ depending on the type and amount of information thatis carried by the DCI.

PDCCH can carry DCI messages associated with multiple users, and each UE115 may decode the DCI messages that are intended for it. For example,each UE 115 may be assigned a cell-radio network temporary identifier(C-RNTI) and cyclic redundancy check (CRC) bits attached to each DCI maybe scrambled based on the C-RNTI. To reduce power consumption andoverhead at the UE, a limited set of CCE locations can be specified forDCI associated with a specific UE 115, which is referred to as a searchspace. CCEs may be grouped (e.g., in groups of 1, 2, 4 and 8 CCEs), anda search space that may include a set of CCE locations in which the UEmay find relevant DCI may be specified. A UE 115 may attempt to decodeDCI by performing a process known as a blind decode, using decodingcandidates associated with different formats of the DCI. In some cases,a control portion of a slot TTI may include a quick PDCCH (QPDCCH),which may information related to slot TTI communications.

Time intervals for communication within wireless communications system100 may be expressed in multiples of a basic time unit (e.g., thesampling period, Ts=1/30,720,000 seconds). Time resources may beorganized according to radio frames of length of 10 ms (Tf=307200 Ts),which may be identified by a system frame number (SFN) ranging from 0 to1023. Each frame may include ten 1 ms subframes numbered from 0 to 9. Asubframe may be further divided into two 0.5 ms slots, each of whichcontains two or more modulation symbol periods (depending on the lengthof the cyclic prefix (CP) prepended to each symbol). Excluding the CP,each symbol contains 2048 sample periods. In various examples, legacy or1 ms TTI communications may use a subframe as the smallest schedulingunit or TTI. Furthermore, as indicated above, wireless communicationssystem 100 may support TTIs having a duration of one subframe as well asshorter duration, such as 0.5 ms or slot TTI (or shorter TTIs), whichmay have a duration of less than one LTE subframe (e.g., one slot). Invarious examples, wireless communications system 100 supports two ormore TTI durations—including a first duration that is at least two LTEsymbol periods in duration, and a second duration that is less than thefirst duration.

Wireless communications system 100 may employ HARQ, a method ofincreasing the likelihood that data is received correctly over awireless communication link 125. HARQ may include a combination of errordetection (e.g., using a CRC), forward error correction (FEC), andretransmission (e.g., automatic repeat request (ARQ)). HARQ may improvethroughput at the MAC layer in poor radio conditions (e.g.,signal-to-noise conditions). In Incremental Redundancy HARQ, incorrectlyreceived data may be stored in a buffer and combined with subsequenttransmissions to improve the overall likelihood of successfully decodingthe data. In some cases, redundancy bits are added to each message priorto transmission. This may be useful in poor conditions. In other cases,redundancy bits are not added to each transmission, but areretransmitted after the transmitter of the original message receives anegative acknowledgement (NACK) indicating a failed attempt to decodethe information. The chain of transmission, response, and retransmissionmay be referred to as a HARQ process, and the total time between atransmission and starting of retransmission of unsuccessfully receiveddata may be referred to as a round trip time (RTT). In some cases, alimited number of HARQ processes may be used for a given communicationlink 125.

In some examples, HARQ processes may be performed at a transport blocklevel, in which the entire transport block is retransmitted when a NACKis received by the transmitter. In a multi-TTI assignment, separateindicators for new data may be used for each transport block (TB) in theassignment. Or, in some examples, a single new data indicator may beused for all TBs of the assignment. In other cases, multi-TTI schedulingmay be used for new transmissions only, such that retransmission may, insome examples, be limited to individual assignments.

In some examples, a transport block may be divided into one or more codeblocks and HARQ processes may be performed at a code block level whereone or more code blocks (e.g., the one or more code blocks that wereunsuccessfully decoded by the receiver) are retransmitted when a NACK isreceived by the transmitter. The threshold for code block level HARQprocesses for low latency TTIs may be different from longer durationTTIs (e.g., it might be different that 6144 bits, as is in LTE).

Some examples may employ different HARQ RTTs for legacy TTIs and forslot TTIs. For example, a HARQ RTT for legacy TTIs may be 8 ms, and aHARQ RTT for slot TTIs may be 4 ms. In other examples, if both lms andslot TTIs are used, the 1 ms HARQ RTT may be 4 ms and the slot TTI HARQRTT may be 2 ms, 3 ms, or 4 ms, depending upon UE capability.

In some cases, wireless communications system 100 may utilize one ormore enhanced component carrier (eCCs). An eCC may be characterized byone or more features including: flexible bandwidth, different TTIdurations, and modified control channel configuration. In some cases, aneCC may be associated with a carrier aggregation (CA) configuration or adual connectivity configuration (e.g., when multiple serving cells havea suboptimal backhaul link). An eCC may also be configured for use inunlicensed spectrum or shared spectrum (e.g., where more than oneoperator is licensed to use the spectrum). An eCC characterized byflexible bandwidth may include one or more segments that may be utilizedby UEs 115 that do are not capable of monitoring the whole bandwidth orprefer to use a limited bandwidth (e.g., to conserve power).

So wireless communications system 100 may concurrently support multiplelatency modes. Available resources and parameters for controlinformation communication according to one latency mode of wirelesscommunications system 100 may be determined with respect to resourcesused for another latency mode of wireless communications system 100. Forexample, a UE 115 may use a search space for 1 ms TTI controlinformation to determine a different search space for slot TTI controlinformation. For example, the search space for slot TTI controlinformation may be a subset of the search space for 1 ms TTI controlinformation, a search space may be determined based on 1 ms TTItechniques and divided up between 1 ms TTI and slot TTI search spaces,or a slot TTI search space may be correlated to the 1 ms TTI searchspace such as through an offset from the 1 ms search space, through aseparate RNTI, through different random seeds, or any combinationthereof. A UE 115 may determine a search space for 1 ms TTI controlinformation and slot TTI control information, and perform blind decodingover the search spaces to identify control information. Scheduling of 1ms or slot TTIs may be UE-specific and may be dynamically orsemi-statically indicated.

FIG. 2 illustrates an example of a wireless communications system 200that supports control channel signaling with multiple TTI lengths.Wireless communications system 200 may include base station 105-a and UE115-a, which may be examples of the corresponding devices described withreference to FIG. 1. Wireless communications system 200 may illustrateaspects of wireless communications system 100. For instance, wirelesscommunications system 200 may include UE 115-a and a base station 105-a,which may be an examples of a UE 115 or base station 105 described withreference to FIG. 1. Base station 105-a may communicate with UE 115-avia communication link 205 and transmit control information to UE 115-afor multiple duration TTIs, as described with reference to FIG. 1.

A frame structure may be used within the wireless communications system200 to organize physical resources. A frame may be a 10 ms interval thatmay be further divided into 10 equally sized subframes or TTIs. Eachsubframe may include two consecutive time slots. Each slot may include 6or 7 OFDMA symbol periods. A resource element consists of one symbolperiod and one subcarrier (e.g., a 15 KHz frequency range). A resourceblock may contain 12 consecutive subcarriers in the frequency domainand, for a normal cyclic prefix in each OFDM symbol, 7 consecutive OFDMsymbols in 1 slot (84 resource elements) in the time domain. Furtherdetails of TTIs that may be utilized by wireless communications system200 are illustrated by and described with reference to FIGS. 3-4.

In some cases, 1 ms length TTI 210 may be an LTE subframe, as well as ashort TTI 215. Short TTI 215 may have a length (i.e., duration) shorterthan fixed length TTI 210, such as 0.5 ms or a slot duration. Short TTIs215 may be employed for low latency operations, in some deployments. Insome cases, using shorter length TTIs may reduce over-the-air latency.For example, short TTIs 215 may help reduce HARQ latency as comparedwith non-low latency TTIs such as 1 ms length TTI 210.

In some examples, slot level short TTIs 215 may follow LTE/LTE-Anumerology, may be backward compatible, and may co-exist with 1-ms LTEtraffic in which transmitted subframes may include both 1 ms TTItransmissions as well as slot TTI transmissions. In some examples, slotlevel TTI may re-use existing broadcast, random access, and handoverprocedures, as well as other procedures of LTE/LTE-A. In some examples,control information for both 1 ms TTI transmissions and slot TTItransmissions may use PDCCH or slot-based ePDCCH (which may be referredto as Quick PDCCH (QPDCCH) or Quick ePDCCH (QePDCCH). In some examples,PHICH in the legacy control region may be used for both slot 0 and slot1 uplink data transmissions. Adjustments to resource allocation,transport block size (TBS) determination, and the link may beimplemented in slot TTI transmissions, in some deployments.

As indicated above, control information for slot-level TTIs may beprovided using PDCCH-based signaling. Various examples described hereinprovide for one or more modifications to PDCCH/ePDCCH-based signaling toprovide control information for slot-level TTIs. In some examples,control transmissions may reuse the legacy control region in slot 0 of asubframe (e.g., PDCCH transmissions in symbol 0 of slot 0). Slot-basedTTI shared channel transmissions (e.g., Quick PDSCH or QPDSCHtransmissions) in slot 0 may be scheduled by QPDCCH. In some examples,QPDCCH transmissions re-use PDCCH CCE structure and may be fullymultiplexed with other legacy control channels. Some examples mayprovide a new DCI to indicate slot 0 and differentiate slot versussubframe TTI scheduling assignments. In other examples, PDCCHtransmissions may include a grant for both subframe TTI assignments andslot TTI assignments for both slots in a subframe. Such techniques mayallow multiplexing of QPDCCH with PDCCH as well as frequency divisionmultiplexing (FDM) of QPDSCH with PDSCH/ePDCCH.

FIG. 3 illustrates an example of a subframe 300 for control channelsignaling with multiple TTI lengths. In some cases, subframe 300 mayinclude 1 ms TTI transmissions and slot TTI transmissions according toaspects of techniques performed by a UE 115 or base station 105 asdescribed with reference to FIGS. 1-2. In the example of FIG. 3,subframe 300 may have a 1 ms duration 305 that corresponds to a 1 ms TTIduration 305. The subframe 300 include slot 0 315, and slot 1 325, whichmay correspond, respectively, to a first slot TTI 310 and a second slotTTI 320. The subframe 300 may be transmitted using a system bandwidth330 and may have 14 symbols, representing a normal CP. A legacy controlregion 335 may occupy a first symbol and an ePDCCH 340 may occupyresources that span both slot 0 315 and slot 1 325, and may includecontrol information for shared channel transmissions, or regular PDSCH370 assigned by PDCCH or ePDCCH. The first slot TTI 310 may includecontrol information for two downlink shared channel assignments throughQePDCCH1 and QePDCCH2 resources 345. In this example, QePDCCH1 maycontain control information for QPDSCH1 350, and QePDCCH2 may containcontrol information for QPDSCH2 355. In the example of FIG. 3, thesecond slot TTI 320 may include control information for a third downlinkshared channel assignment and an uplink assignment, through QePDCCH3(for DL) and QePDCCH4 (for UL) resources 360. In this example, QePDCCH3may contain control information for QPDSCH 365 of slot 1 325, andQePDCCH4 may contain control information for an associated uplinktransmission. Thus, in this example, FDM with QePDCCH and QPDSCH isprovided.

In other examples, FDM may be used for PDCCH, QPDCCH, and QPDSCHtransmissions. FIG. 4 illustrates such an example, with a subframe 400for control channel signaling with multiple TTI lengths. In some cases,subframe 400 may include 1 ms TTI transmissions and slot TTItransmissions according to aspects of techniques performed by a UE 115or base station 105 as described with reference to FIGS. 1-2. In theexample of FIG. 4, subframe 400 may have a 1 ms duration 405 thatcorresponds to a 1 ms TTI duration 405. The subframe 400 include slot 0415, and slot 1 425, which may correspond, respectively, to a first slotTTI 410 and a second slot TTI 420. The subframe 400 may be transmittedusing a system bandwidth 430 and may have 14 symbols, representing anormal CP.

In this example, symbol 0 of slot 0 415 may include PDCCH, legacycontrol, and QPDCCH resources 435, which may be allocated resourcesusing FDM. An ePDCCH 440 may occupy resources that span both slot 0 415and slot 1 425, and may include control information for shared channeltransmissions, or regular PDSCH 460 assigned by PDCCH or ePDCCH. Thefirst slot TTI 410 may include QPDSCH resources 445 that may be assignedin the QPDCCH. In the example of FIG. 4, the second slot TTI 420 mayinclude control information in QePDCCH1 resources 450. In this example,QePDCCH1 450 may contain control information for QPDSCH1 455 of slot 1425. Thus, in this example, FDM with PDCCH, QPDCCH, QePDCCH and QPDSCHresources is provided.

FIG. 5 illustrates an example of UL and DL transmissions 500 thatsupport multiple TTIs and associated control channel signaling. In somecases, UL and DL transmissions 500 may represent aspects of techniquesperformed by a UE 115 or base station 105 as described with reference toFIGS. 1-2. FIG. 5 also illustrates HARQ timing and RTT associated with 1ms TTIs and slot TTIs according to some examples. In legacy LTE, HARQfeedback for a transmission may be provided in a first available TTIthat is n+4 TTIs away from a TTI (TTI n) that includes the transmissionassociated with the HARQ feedback. Thus, legacy LTE, and in someexamples 1 ms TTI transmissions, may have a HARQ RTT of 8 ms. In someexamples, slot TTI transmissions may follow the same relationship fortransmission of HARQ feedback and subsequent retransmissions, and thusprovide linear scaling and a HARQ RTT of 4 ms.

In the example, of FIG. 5, base station 105-b may transmit DLtransmissions 505, and UE 115-b may transmit UL transmissions 510. TheDL transmissions 505 and UL transmissions 510 may include both 1 ms TTItransmissions as well as slot TTI transmissions. In this example,subframe 0 may include sot 0 and slot 1, which may include QPDSCH DLtransmissions 525 that may include a first slot transmission 515 in slot0 and a second slot transmission 520 in slot 1. The DL transmissions 505may include PDSCH transmission 530 that may use a 1 ms TTI. As indicatedabove, UE 115-b may receive QPDSCH transmissions 525 and provide HARQfeedback. In this example, QPUCCH ACK/NACK transmissions 535 may betransmitted by UE 115-b four slots after the associated QPDSCHtransmission 525. The base station 105-b may receive the QPUCCH ACK/NACKtransmissions 535 and transmit, if needed, QPDSCH retransmission 540 ofdata having a NACK feedback. Because the slot TTI length is one-half the1 ms TTI length, the low latency (LL) HARQ RTT 545 of this example is 4ms, one-half of the 1 ms RTT. Likewise, 1 ms TTI PDSCH transmission 530may be received at UE 115-b which may provide PUCCH ACK/NACK feedback550 according to legacy LTE HARQ timelines. The base station 105-b mayreceive the PUCCH ACK/NACK transmissions 550 and transmit, if needed,PDSCH retransmission 555 of data having a NACK feedback, according tolegacy timelines thus providing a HARQ RTT 560 of 8 ms. Thus, slot TTItransmissions may have a reduced HARQ RTT, and may thus provide lowerlatency for HARQ feedback and associated retransmissions.

In some examples, instead of a factor of 2 (8 ms vs. 4 ms) reduction inHARQ RTT, additional reduction of HARQ RTT may be configured. FIG. 6illustrates such an example, showing UL and DL transmissions 600 thatsupport multiple TTIs and associated control channel signaling. In somecases, UL and DL transmissions 600 may represent aspects of techniquesperformed by a UE 115 or base station 105 as described with reference toFIGS. 1-2. FIG. 6 also illustrates HARQ timing and RTT associated with 1ms TTIs, with further reduced slot TTI HARQ RTT. In this example, slotTTI transmissions may provide for transmission of HARQ feedback withonly one TTI separating a DL transmission and an ACK/NACK feedbackindication, and with one TTI separating receipt of ACK/NACK feedback anda retransmission. Thus, in such examples, slot TTI transmission may beprovided with a HARQ RTT of 2 ms.

In the example, of FIG. 6, base station 105-c may transmit DLtransmissions 605, and UE 115-c may transmit UL transmissions 610. TheDL transmissions 605 and UL transmissions 610 may include both 1 ms TTItransmissions as well as slot TTI transmissions. In this example,subframe 0 may include sot 0 and slot 1, which may include QPDSCH DLtransmissions 625 that may include a first slot transmission 615 in slot0 and a second slot transmission 620 in slot 1. The DL transmissions 605may include PDSCH transmission 630 that may use a 1 ms TTI. As indicatedabove, UE 115-c may receive QPDSCH transmissions 625 and provide HARQfeedback. In this example, QPUCCH ACK/NACK transmissions 635 may betransmitted by UE 115-c with a one TTI, or one slot gap, after theassociated QPDSCH transmission 625. The base station 105-c may receivethe QPUCCH ACK/NACK transmissions 635 and transmit, if needed, QPDSCHretransmission 640 of data having a NACK feedback. Because the slot TTIlength is 0.5 ms, the LL HARQ RTT 645 of this example is 2 ms. Similarlyas discussed with respect to FIG. 5, 1 ms TTI PDSCH transmission 630 maybe received at UE 115-c which may provide PUCCH ACK/NACK feedback 650according to legacy LTE HARQ timelines. The base station 105-c mayreceive the PUCCH ACK/NACK feedback 650 and transmit, if needed, PDSCHretransmission 655 of data having a NACK feedback, according to legacytimelines thus providing a HARQ RTT 660 of 8 ms. Such a HARQ timelinemay provide more challenging requirements for processing at the UE 115-cand base station 105-c, and in some examples a UE may be configured fora shorter HARQ RTT based on capabilities of the UE. Such a HARQ timelinefor slot TTI may also result in more limitation on possible UL timingadvance (which effectively reduces the processing time) and hence thecoverage area for such examples may be reduced relative to coverageareas available for longer HARQ timelines.

As indicated above, a 2 ms HARQ timeline may provide processingchallenges to some UEs, and also may result in a reduced coverage area.In some examples, a slot TTI HARQ timeline may be selected based onparticular UE capabilities, coverage area requirements, particulartraffic at a given time, other factors, or any combination thereof. Forexample, a 3 ms HARQ RTT may be configured for slot TTI communications.FIG. 7 illustrates an example of such UL and DL transmissions 700. Insome cases, UL and DL transmissions 700 may represent aspects oftechniques performed by a UE 115 or base station 105 as described withreference to FIGS. 1-2. FIG. 7 also illustrates HARQ timing and RTTassociated with 1 ms TTIs, with further reduced slot TTI HARQ RTT. Inthis example, slot TTI transmissions may provide a HARQ timeline of 3ms.

In the example, of FIG. 7, base station 105-d may transmit DLtransmissions 705, and UE 115-d may transmit UL transmissions 710. TheDL transmissions 705 and UL transmissions 710 may include both 1 ms TTItransmissions as well as slot TTI transmissions. In this example,subframe 0 may include sot 0 and slot 1, which may include QPDSCH DLtransmissions 725 that may include a first slot transmission 715 in slot0 and a second slot transmission 720 in slot 1. The DL transmissions 705may include PDSCH transmission 730 that may use a 1 ms TTI. As indicatedabove, UE 115-d may receive QPDSCH transmissions 725 and provide HARQfeedback. In this example, QPUCCH ACK/NACK transmissions 735 may betransmitted by UE 115-d with a two TTI, or two slot gap, after theassociated QPDSCH transmission 725. The base station 105-d may receivethe QPUCCH ACK/NACK transmissions 735 and transmit, if needed, QPDSCHretransmission 740 of data having a NACK feedback. Because the slot TTIlength is 0.5 ms, the LL HARQ RTT 745 of this example is 3 ms. Similarlyas discussed with respect to FIG. 5, 1 ms TTI PDSCH transmission 730 maybe received at UE 115-d which may provide PUCCH ACK/NACK feedback 750according to legacy LTE HARQ timelines. The base station 105-d mayreceive the PUCCH ACK/NACK feedback 750 and transmit, if needed, PDSCHretransmission 755 of data having a NACK feedback, according to legacytimelines thus providing a HARQ RTT 760 of 8 ms. Such a HARQ timelinemay provide more relaxed requirements for processing at the UE 115-d andbase station 105-d relative to the 2 ms RTT of the example of FIG. 6,and in some examples a UE may be configured for such a HARQ RTT based oncapabilities of the UE.

In further examples, HARQ RTT for 1 ms TTI transmissions may also bemodified. For example, slot TTI transmissions may be configured with areduced HARQ RTT, and 1 ms TTI transmissions also may be configured witha reduced HARQ RTT. FIG. 8 illustrates such an example of UL and DLtransmissions 800 that support multiple TTIs and associated controlchannel signaling. In some cases, UL and DL transmissions 800 mayrepresent aspects of techniques performed by a UE 115 or base station105 as described with reference to FIGS. 1-2. FIG. 8 also illustratesreduced HARQ timing and RTT associated with 1 ms TTIs, with furtherreduced slot TTI HARQ RTT. In this example, both slot TTI and 1 ms TTItransmissions may provide for transmission of HARQ feedback with onlyone TTI separating a DL transmission and an ACK/NACK feedbackindication, and with one TTI separating receipt of ACK/NACK feedback anda retransmission. Thus, in such examples, slot TTI transmission may beprovided with a HARQ RTT of 2 ms, and 1 ms TTI transmissions may beprovided with a HARQ RTT of 4 ms.

In the example, of FIG. 8, base station 105-e may transmit DLtransmissions 805, and UE 115-e may transmit UL transmissions 810. TheDL transmissions 805 and UL transmissions 810 may include both 1 ms TTItransmissions as well as slot TTI transmissions. In this example,subframe 0 may include sot 0 and slot 1, which may include QPDSCH DLtransmissions 825 that may include a first slot transmission 815 in slot0 and a second slot transmission 820 in slot 1. The DL transmissions 805may include PDSCH transmission 830 that may use a 1 ms TTI. As indicatedabove, UE 115-e may receive QPDSCH transmissions 825 and provide HARQfeedback. In this example, QPUCCH ACK/NACK transmissions 835 may betransmitted by UE 115-e with a one TTI, or one slot gap, after theassociated QPDSCH transmission 825. The base station 105-e may receivethe QPUCCH ACK/NACK transmissions 835 and transmit, if needed, QPDSCHretransmission 840 of data having a NACK feedback. Because the slot TTIlength is 0.5 ms, the LL HARQ RTT 845 of this example is 2 ms. Further,in this example, 1 ms TTI PDSCH transmission 830 may be received at UE115-e which may provide PUCCH ACK/NACK feedback 850 with a one TTI, orone subframe gap, after the associated PDSCH transmission 830. The basestation 105-e may receive the PUCCH ACK/NACK transmissions 850 andtransmit, if needed, PDSCH retransmission 855 of data having a NACKfeedback, one TTI or one subframe following the PUCCH ACK/NACKtransmissions 850, thus providing a HARQ RTT 860 of 4 ms. Such a HARQtimeline may provide lower latency for both 1 ms and slot TTItransmissions.

In some examples, a single DL HARQ timeline may be configured forslot-level TTI, which may be selected based on latency requirements, UEcapabilities, and the like. The corresponding legacy PDSCH timeline maystill be legacy (8 ms) or reduced (e.g., 4 ms), which configurable on aper UE basis. In some examples, the modified 1 ms TTI HARQ timeline maybe implemented for PDSCH transmissions scheduled from the UE-specificsearch space. In other examples, multiple DL HARQ timelines may beconfigured for multiple different UEs, and a particular HARQ timelinemay be based on UE capability, operating conditions, channel conditions,traffic conditions, or any combination thereof. For example, if twoslot-TTI HARQ timelines are available, such as a 2 ms RTT and 4 ms RTT,a UE may indicate its capability to a base station. If the UE indicates4 ms RTT capability, the base station may configure that UE for 4 msRTT. For a UE indicating capability for 2 ms RTT for slot-level TTI, theUE can be configured by the base station to use either 2 ms or 4 ms RTTfor slot-TTI. In some examples, a UE can be further configured suchthat, if 2 ms RTT for slot-level TTI is configured, either a 4 ms RTT ora 8 ms RTT is to be used for 1-ms based TTI.

As discussed above, a base station (e.g., base station 105 of FIGS. 1-8)may transmit control information for 1 ms TTI and slot TTI transmissionsusing downlink control channels. As also indicated above, a UE mayperform blind decoding over a search space to identify the controlinformation. In some examples, blind decoding for QPDCCH or QePDCCHtransmissions may be configured to provide UEs with reliable decodingfor slot TTI control information. In some examples, due to relativelyhigh processing requirements based on slot TTI timelines, blind decodingof DCI information and format may be provided that requires no or littlepruning to rule out false alarms. In legacy PDCCH, for example, a UE mayperform up to 44 blind decodes (w/o UL MIMO) or 60 blind decodes (w/ ULMIMO) per CC. Additionally, for eCA examples with up to 32 CCsconfigured for a UE, the decoding candidates for a UE can be reduced andhigher-layer configured on a per UE basis, in light of UE capability forperforming blind decodes within timelines. In some examples, slot TTIcontrol channels may be provided with a limited set of decodingcandidates, limited possible DCI size(s), or any combination thereof.For example, a slot TTI may be configured to have a limited set ofaggregation levels and limited number of decoding candidates for eachaggregation level. Decoding candidates may be configured on a UE basisfor each CC, in some examples. For example, a UE may be configured witha set of decoding candidates and a restriction on DCI format(s) (e.g.,no more than 6 decoding candidates per slot and only one DCI format).

In some examples, a UE may be configured with a HARQ RTT-dependentrestriction of decoding candidates. For example, if a UE is configuredto have 1 ms TTI transmissions with a 4 ms HARQ RTT, a number of blinddecodes may be reduced from the original 44/60 blind decodes, and forslot TTI transmissions there may be separate restrictions of decodingcandidates for 2 ms HARQ RTT and 4 ms HARQ RTT. In further examples, abase station may configure restricted blind decoding candidates for 1-msTTI transmissions (PDCCH or ePDCCH) when slot-level TTI is configuredfor the UE. For example, if a CC is configured without slot TTI, the UEmay be configured to perform up to 44/60 blind decodes for PDCCH/ePDCCH,but if slot TTI is configured the UE may be configured to perform up to32/48 blind decodes for PDCCH/ePDCCH in a subframe for a CC and up to 6blind decodes for QPDCCH/QePDCCH in each slot of a subframe for a CC,thus keeping the total number of blind decodes at a same level. Inanother example, legacy TTI DCIs may be only monitored in a commonsearch space, while a UE-specific search space may only carry slot-TTIbased DCIs.

Also as discussed above, in some examples a search space for 1 ms TTIcontrol information and slot TTI control information may be configuredto provide a UE with search spaces for receiving control information.For legacy PDCCH/ePDCCH transmissions, a search space may be derived bya UE's C-RNTI, random seeds, and the total control space size, and mayalso be a function of aggregation level. In some examples, slot TTIcontrol information may follow a similar same mechanism forQPDCCH/QEPDCH transmissions. In certain examples, QPDCCH and PDCCH mayhave a correlated search space, in which the search space for QPDCCH isdetermined based on an identified search space for PDCCH. In someexamples, the decoding candidates for QPDCCH may be a subset of thosefor PDCCH. In some examples, the original search space for PDCCH can besplit to two parts, one for 1-ms TTI, and one for slot TTI. Having sucha correlated search space for QPDCCH and PDCCH may help reducecomplexity at a UE, as a collection of samples can be used for decodingfor both QPDCCH and PDCCH. Thus, the search space defined for PDCCH canbe used for both PDCCH and QPDCCH, but different restrictions of the setof candidates to monitor for PDCCH and QPDCCH can be defined, includingpossibly different DCI sizes and/or formats. In other examples, aseparate search space may be configured for QPDCCH and PDCCH, such as byhaving the QPDCCH search space offset with respect to the PDCCH searchspace, or generated by a separate radio network temporary (RNTI) and/ordifferent random seeds. Such correlation of search spaces may bepossible for slot 0 transmissions, but not for slot 1 transmissionsbecause there is no legacy PDCCH search space in slot 1. Thus, for slot1, the QPDCCH search space may be different that of PDCCH, as will bediscussed in further detail below with reference to FIG. 9. It is to benoted that the correlation of search space is also applicable to ePDCCHand QePDCCH.

As mentioned earlier, in some examples a single DCI format may beconfigured per link (DL or UL). For example, a UE may be configured tomonitor DCI format 1A for 1 ms TTI, and to monitor a mode-dependent DCIformat for slot TTI. In some examples, a separate DCI format may beprovided for slot TTI control information. The DCI size for slot TTI maybe smaller than that of legacy control channels, as a resourceallocation size may be smaller (e.g., in a 20 MHz system). For example,for contiguous resource allocation, legacy DCI format 1A resourceallocation size is log2((100+1)*100/2), which is 13 bits. If slot TTI isconfigured with a 2-RB resource allocation granularity, the resourceallocation size may be log2((50+1)/50), which is 11 bits (2 bits lessthan 1 ms TTI). For bit-map based resource allocation, the legacyresource allocation needs 25 bits (each bit indicates a RB group (RBG)of 4 RBs), and for slot-TTI such a resource allocation may be 13 bits ifa new RB group is 8 RBs, which results in a 12-bit reduction. In someexamples, the RBG size for slot-TTI may also be configurable ordynamically indicated. Further DCI size reductions may come from notusing transmit power control (TPC) in slot TTI DCI, and relying on thelegacy DCI for power control, which may result in two fewer bits in slotTTI DCI. Additionally, the 5-bit MCS in legacy DCI may be reduced to a3-bit MCS in some examples. In such examples, the three bits may bemapped to different MCS values and may be specifically configured perUE, and such mapping may be updated periodically (e.g., via radioresource control (RRC) signaling or a SIB). Furthermore, the 2-bitredundancy version of legacy DCI may be omitted or reduced to one-bit,and if configured with a 2 ms HARQ RTT only a 2-bit HARQ process ID isnecessary (vs. legacy 3-bit). Thus, the DCI for slot TTI may be reducedfrom the DCI size of legacy 1 ms TTI.

In some examples, a same DCI size may be used for both 1-ms TTI and slotTTI control information, with some of the 1 ms TTI information fieldsre-interpreted to provide additional or different information. In suchcases, differentiation of whether a DCI schedules a 1-ms TTI or a slotTTI can be based on search space (e.g., a DCI in common search space isfor 1-ms TTI, while a DCI in UE-specific search space is for slot TTI),an indication in the DCI, or any combination thereof. In one example,the slot TTI DCI format may include an indication of scheduling slot 0,slot 1, or slot 0 and slot 1, each with slot TTI, or a 1-ms TTI. Infurther examples, the slot TTI DCI may use a 24-bit CRC (instead of16-bit CRC for 1 ms TTI DCI). Such an increased CRC size may beaccommodated by the fewer bits for slot TTI DCI, as discussed above, andmay reduce or eliminate the need for a UE to perform pruning to reducefalse alarm likelihood.

As mentioned above, QPDCCH in the second slot may be configuredseparately than QPDCCH in the first slot. Because there is no legacycontrol in the second slot, and legacy PDSCH may utilize this slot,QPDCCH in the second slot, in various examples, is configured toco-exist with legacy PDSCH. For example, PBCH may be present in thecenter 6 RBs of the first to fourth symbols of the second slot insubframe 0 of every frame. Furthermore, a cell-specific reference signal(CRS) may be present only in the data region of the second slot of amulticast-broadcast single-frequency network (MBSFN) subframe, thusmaking CRS-based QPDCCH more difficult to support. In some examples,instead of defining the second slot search space over the entire systembandwidth as in PDCCH or QPDCCH in the first slot, the QPDCCH searchspace in the second slot may be defined based on a set of RBs configuredby the base station. Such RBs may or may not collide with PBCH, and inthe case of time division duplexing (TDD) may or may not collide with aSSS in the last symbol of subframes 0 and 5. In the event that adecoding candidate collides with PBCH or SSS, the candidate may beomitted for monitoring. Such a configuration may be based on a bitmapwith one RB, or RBG, granularity.

In some examples, one or more sets of RBs may be configured for QPDCCHin the second slot, in a similar manner as ePDCCH. For example, up totwo sets of RBs may be configured for a UE, where each set mayself-contain a search space monitored by a UE. In some examples, a REGbased solution may be used, in a similar manner as to legacy PDCCH. Insome examples, two modes may be supported, one distributed in which aCCE is mapped to REGs of different RBs as much as possible, which mayprovide enhanced robustness and frequency diversity. The other mode maybe a localized mode, where a CCE is mapped to REGs of s smaller numberof RBs as much as possible, which may provide more efficientmultiplexing with QPDSCH and PDSCH. The time span of control informationresources (e.g., number of symbols) for QPDCCH may be predefined in someexamples (e.g,. only 1 symbol, symbol 0), may be layer 3 configured(e.g., symbol 0 only, symbol0+symbol1, etc.), or dynamically indicated.Furthermore, in some cases the time span of the control information maybe different for different sets of RBs when two or more sets of RBs areconfigured. Additionally or alternatively, the time span may be tiedwith HARQ RTT. For example, if 2 ms RTT is configured, the time span maybe limited to no more than the first 3 symbols, but if 4 ms RTT isconfigured the time span may be up to 7 symbols or the entire slot.

While various of the above examples are directed to PDCCH and QPDCCH (orePDCCH/QePDCCH), other control channels also may be present in thesecond slot in slot TTIs. For example, PCFICH may be in the second slotin some examples, while in other examples may not be present in thesecond slot. In examples where PCFICH is in the second slot, it may usethe same mechanism as that of the PCFICH in the first slot. In someexamples, the RBs configured for PCFICH in the second slot may be basedon a RRC configuration instead of based on the entire system bandwidth(e.g., the PCFICH RE locations can be implicitly derived based on theset of RBs configured for QPDCCH). In certain examples, two sets ofQPDCCH may be configured at a UE, and each set may have its own PCFICH.Some examples may utilize legacy PCFICH in both the first slot andsecond slot, and the control region in each of the slots may be thesame. In some cases, a base station may balance the control channel for1-ms TTI UES and slot TTI UEs in the first slot and the second slot toprovide good alignment of the control region size (e.g., the number ofsymbols for control). In some examples, PHICH may be present in thefirst slot but not the second slot, which may allow for asynchronous ULHARQ for slot TTI communications.

FIG. 9 illustrates an example of a subframe 900 for control channelsignaling with multiple TTI lengths. In some cases, subframe 900 mayrepresent aspects of techniques performed by a UE 115 or base station105 as described with reference to FIGS. 1-8. In the example of FIG. 9,multiplexing with QPDSCH resources may include pure time divisionmultiplexing (TDM) or TDM/FDM, depending upon the slot.

As illustrated in FIG. 9, subframe 900 may include a first slot 905 anda second slot 910. The first slot 905 may include RBs occupied by aQPDCCH transmission in 915 that are located in a first symbol 935 offirst slot 905. In the first slot 905, the first symbol 935 may includeonly control information, and RBs occupied by a PDSCH transmission 920in the first slot may be located only following the first symbol 935 ofthe first slot. Thus, control information in the first slot 905 may bein a purely TDM relationship with shared channel data in the first slot905. In the second slot 910, RBs occupied by a QPDCCH transmission 925may be located in a first symbol 940 of the second slot 910, and RBsoccupied by a QPDSCH transmission 930 may be in a FDM relationship withQPDCCH transmissions in this symbol. Thus, RBs occupied by a QPDCCHtransmission 925 may be multiplexed with RBs occupied by a QPDSCHtransmission 930 using both TDM and FDM. Such a multiplexing schemeimplies that a QPDSCH may have different start symbols in different RBs.In some cases, for RBs not part of the RBs configured as part of theQPDCCH search space in the second slot 910, QPDSCH can always start fromthe first symbol 940 of the second slot 910. In other cases, for RBsoccupied by the corresponding QPDCCH, QPDSCH can start in a symbolimmediately after the last symbol of the corresponding QPDCCH. Infurther cases, for RBs not occupied by the corresponding QPDCCH, butpart of the RBs configured for QPDCCH search space in the second slot,the starting symbol can follow either of the other cases, and in someexamples, a base station may dynamically or semi-statically indicatewhether QPDSCH can start from the first symbol 940 of the second slot910 or after the last symbol of the configured QPDCCH search space. Inanother example, a starting symbol for a RB for QPDSCH may also beconfigured by higher layers. Note that it is possible that a first groupof RBs may be configured with a first starting symbol, while a secondgroup of RBs may be configured with a second start symbol. Themanagement of starting symbol may also be applicable to QePDCCH. Forexample, two sets of QePDCCH resources may be configured, and each setmay be further associated with a respective starting symbol configuredby the base station.

FIG. 10 illustrates an example of a process flow 1000 for controlchannel signaling with multiple TTI lengths in accordance with variousaspects of the present disclosure. Process flow 1000 may include basestation 105-f and UE 115-f, which may be examples of the correspondingdevices described with reference to FIG. 1-9.

At block 1005, the base station 105-f may configure TTIs and searchspaced for each TTI. Base station 105-f may, for example, configure both1 ms TTIs and slot TTIs for UE 115-f, and may configure a search spacefor control information of the slot TTIs to be correlated to a searchspace for 1 ms TTIs. The base station 105-f may transmit theconfiguration information 1010 to UE 115-f. The UE 115-f may, at block1015, identify the first and second TTIs, such as 1 ms TTIs and slotTTIs. The UE 115-f at block 1020 may then identify a first search spaceassociated with the first TTI (e.g., a search space for the 1 ms TTI).At block 1025, the UE 115-f may determine a second search space, whichmay be determined based at least in part on the first search space, insome examples.

At block 1030, the base station 105-f may format downlink transmissionsaccording to the first TTI and the second TTI, and may transmit downlinktransmissions 1035. The UE may monitor the first search space and/or thesecond search space for DL transmissions, and at block 1040, the UE115-f may blind decode the first and second search spaces for controlinformation associated with the different TTI transmissions. Based ondecoded control information for transmissions of each TTI, the UE 115-fat block 1045 may decode shared channel transmissions. At optional block1050, the UE 115-f may determine HARQ feedback associated with theshared channel transmissions and transmit the HARQ feedback 1055 to thebase station 105-f, in a manner as discussed above with respect to FIGS.5-8.

FIG. 11 shows a block diagram of a wireless device 1100 that supportscontrol channel signaling with multiple TTI lengths in accordance withvarious aspects of the present disclosure. Wireless device 1100 may bean example of aspects of a UE 115 described with reference to FIGS. 1and 2. Wireless device 1100 may include receiver 1105, controlinformation manager 1110 and transmitter 1115. Wireless device 1100 mayalso include a processor. Each of these components may be incommunication with each other.

The receiver 1105 may receive information such as packets, user data, orcontrol information associated with various information channels (e.g.,control channels, data channels, and information related to controlchannel signaling with multiple TTI lengths, etc.). Information may bepassed on to other components of the device. The receiver 1105 may be anexample of aspects of the transceiver 1425 described with reference toFIG. 14.

The control information manager 1110 may identify a first TTI having afirst duration that comprises two or more symbol periods and a secondTTI having a second duration that is less than the first duration,identify a first search space for monitoring for first controlinformation associated with the first TTI, determine, based on the firstsearch space, a second search space for monitoring for second controlinformation associated with the second TTI, and monitor at least one ofthe first search space for the first control information or the secondfor the second control information. The control information manager 1110may also be an example of aspects of the control information manager1405 described with reference to FIG. 14.

The transmitter 1115 may transmit signals received from other componentsof wireless device 1100. In some examples, the transmitter 1115 may becollocated with a receiver in a transceiver module. For example, thetransmitter 1115 may be an example of aspects of the transceiver 1425described with reference to FIG. 14. The transmitter 1115 may include asingle antenna, or it may include a plurality of antennas.

FIG. 12 shows a block diagram of a wireless device 1200 that supportscontrol channel signaling with multiple TTI lengths in accordance withvarious aspects of the present disclosure. Wireless device 1200 may bean example of aspects of a wireless device 1100 or a UE 115 describedwith reference to FIGS. 1, 2 and 11. Wireless device 1200 may includereceiver 1205, control information manager 1210 and transmitter 1225.Wireless device 1200 may also include a processor. Each of thesecomponents may be in communication with each other.

The receiver 1205 may receive information which may be passed on toother components of the device. The receiver 1205 may also perform thefunctions described with reference to the receiver 1105 of FIG. 11. Thereceiver 1205 may be an example of aspects of the transceiver 1425described with reference to FIG. 14.

The control information manager 1210 may be an example of aspects ofcontrol information manager 1110 described with reference to FIG. 11.The control information manager 1210 may include TTI duration component1215 and search space component 1220. The control information manager1210 may be an example of aspects of the control information manager1405 described with reference to FIG. 14.

The TTI duration component 1215 may identify a first TTI having a firstduration that comprises two or more symbol periods and a second TTIhaving a second duration that is less than the first duration.

The search space component 1220 may identify a first search space formonitoring for first control information associated with the first TTI,and determine, based on the first search space, a second search spacefor monitoring for second control information associated with the secondTTI. In some examples, the first and second search spaces may be locatedin a first slot of a subframe, and the search space component maydetermine a third search space in a second slot for monitoring for thesecond subset of second control information,

In some cases, the second search space is a subset of the first searchspace. In some cases, the determining the second search space comprises:deriving the second search space based on one or more of a second UEnetwork identifier or a random seed. In some cases, the first controlinformation comprises first DCI having a first DCI size and a first DCIformat, and the second control information comprises second DCI having asecond DCI size and a second DCI format, and where one or more of thefirst DCI size and the second DCI size or the first DCI format and thesecond DCI format is different.

In some cases, the first DCI size is larger than the second DCI size. Insome cases, the first DCI size and second DCI size are the same, andwhere one or more bits of the second DCI provide different informationthan corresponding bits in the first DCI. In some cases, the first DCIincludes a first number of CRC bits, and the second DCI includes asecond number of CRC bits that is greater than the first number of CRCbits. In some cases, the second control information comprises a firstsubset of second control information transmitted in a first slot of awireless transmission subframe and a second subset of second controlinformation transmitted in a second slot of the wireless transmissionsubframe.

In some cases, the first subset transmitted in the first slot of thewireless transmission subframe is transmitted in a control channel thatis time division multiplexed with shared channel data transmissions inthe first slot, and the second subset transmitted in the second slot ofthe wireless transmission subframe is transmitted in a second controlchannel that is both time division multiplexed and frequency divisionmultiplexed with shared channel data transmissions in the second slot.In some cases, the third search space is determined based on a set ofRBs of the second slot configured for control information transmissions.

In some cases, the first search space and second search space aredistributed over a system bandwidth for transmissions in the first slot,and where the third search space is distributed over a subset of thesystem bandwidth. In some cases, the third search space is determinedbased on a transmission mode associated with the second controlinformation. In some cases, the second subset of second controlinformation comprises one or more of PDCCH information or PCFICHinformation transmitted in a second slot of the wireless transmissionsubframe. In some cases, the second search space is correlated to thefirst search space.

The transmitter 1225 may transmit signals received from other componentsof wireless device 1200. In some examples, the transmitter 1225 may becollocated with a receiver in a transceiver module. For example, thetransmitter 1225 may be an example of aspects of the transceiver 1425described with reference to FIG. 14. The transmitter 1225 may utilize asingle antenna, or it may utilize a plurality of antennas.

FIG. 13 shows a block diagram of a control information manager 1300which may be an example of the corresponding component of wirelessdevice 1100 or wireless device 1200. That is, control informationmanager 1300 may be an example of aspects of control information manager1110 or control information manager 1210 described with reference toFIGS. 11 and 12. The control information manager 1300 may also be anexample of aspects of the control information manager 1405 describedwith reference to FIG. 14.

The control information manager 1300 may include decoding candidatecomponent 1305, search space component 1310, TTI duration component1315, decoder 1320, HARQ component 1325 and multiplexing component 1330.Each of these modules may communicate, directly or indirectly, with oneanother (e.g., via one or more buses).

The decoding candidate component 1305 may identify a first subset of thedecoding candidates as being in the first search space, and identify aset of blind decoding candidates for blind decoding transmissionsreceived in the first and second search spaces. The set of blinddecoding candidates may be based on one or more of an available numberof aggregation levels for second TTI transmissions, an available DCIformat for the second control information. In some examples, thedecoding candidate component 1305 may identify a set of blind decodingcandidates for blind decoding transmissions received in the secondsearch space based on a RTT for HARQ feedback associated with the secondcontrol information.

In some cases, the identifying the first search space comprises:deriving a set of decoding candidates for decoding of received wirelesstransmissions and identification of the first control information andthe second control information. In some cases, the determining thesecond search space comprises: identifying a second subset of thedecoding candidates as being in the second search space. In some cases,the first subset of decoding candidates and the second subset ofdecoding candidates are non-overlapping subsets of the set of decodingcandidates. In some cases, the deriving is based on one or more of a UEnetwork identifier, a random seed, or a total size available for controlinformation. In some cases, a different set of blind decoding candidatesfor the first search space is identified when transmissions using thesecond TTI are configured than when transmissions using the second TTIare not configured.

The search space component 1310 may determine a third search space inthe second slot for monitoring for the second subset of second controlinformation, identify a first search space for monitoring for firstcontrol information associated with the first TTI, and determine, basedon the first search space, a second search space for monitoring forsecond control information associated with the second TTI.

The TTI duration component 1315 may identify a first TTI having a firstduration that comprises two or more symbol periods and a second TTIhaving a second duration that is less than the first duration.

The decoder 1320 may blind decode wireless transmissions received in thefirst search space for the first control information, and blind decodewireless transmissions received in the second search space for thesecond control information.

The HARQ component 1325 may identify a first RTT for HARQ feedbackassociated with the first control information, and identify a second RTTfor HARQ feedback associated with the second control information, wherethe second RTT is shorter than the first RTT. In some cases, the secondRTT is determined based on a capability of a UE receiving the secondcontrol information. In some cases, the first RTT is determined to be alegacy RTT or a shorter RTT than the legacy RTT based on a capability ofthe UE.

The multiplexing component 1330 may determine a starting symbol for theshared channel data transmissions in the second slot based on one ormore of a configured starting symbol location or a symbol location ofthe second subset of second control information, and determine astarting symbol for the shared channel data transmissions in the secondslot based on the third search space.

FIG. 14 shows a diagram of a system 1400 including a device thatsupports control channel signaling with multiple TTI lengths inaccordance with various aspects of the present disclosure. For example,system 1400 may include UE 115-g, which may be an example of a wirelessdevice 1100, a wireless device 1200, or a UE 115 as described withreference to FIGS. 1 through 13.

UE 115-g may also include control information manager 1405, memory 1410,processor 1420, transceiver 1425, antenna 1430 and ECC module 1435. Eachof these modules may communicate, directly or indirectly, with oneanother (e.g., via one or more buses). The control information manager1405 may be an example of a control information manager as describedwith reference to FIGS. 11 through 13.

The memory 1410 may include random access memory (RAM) and read onlymemory (ROM). The memory 1410 may store computer-readable,computer-executable software including instructions that, when executed,cause the processor to perform various functions described herein (e.g.,control channel signaling with multiple TTI lengths, etc.). In somecases, the software 1415 may not be directly executable by the processorbut may cause a computer (e.g., when compiled and executed) to performfunctions described herein. The processor 1420 may include anintelligent hardware device, (e.g., a central processing unit (CPU), amicrocontroller, an application specific integrated circuit (ASIC),etc.)

The transceiver 1425 may communicate bi-directionally, via one or moreantennas, wired, or wireless links, with one or more networks, asdescribed above. For example, the transceiver 1425 may communicatebi-directionally with a base station 105 or a UE 115. The transceiver1425 may also include a modem to modulate the packets and provide themodulated packets to the antennas for transmission, and to demodulatepackets received from the antennas. In some cases, the wireless devicemay include a single antenna 1430. However, in some cases the device mayhave more than one antenna 1430, which may be capable of concurrentlytransmitting or receiving multiple wireless transmissions.

The ECC module 1435 may enable operations using ECCs such ascommunication using shared or unlicensed spectrum, using reduced lengthTTIs or subframe durations, or using a large number of CCs.

FIG. 15 shows a flowchart illustrating a method 1500 for control channelsignaling with multiple TTI lengths in accordance with various aspectsof the present disclosure. The operations of method 1500 may beimplemented by a device such as a UE 115 or its components as describedwith reference to FIGS. 1 and 2. For example, the operations of method1500 may be performed by the control information manager as describedherein. In some examples, the UE 115 may execute a set of codes tocontrol the functional elements of the device to perform the functionsdescribed below. Additionally or alternatively, the UE 115 may performaspects the functions described below using special- purpose hardware.

At block 1505, the UE 115 may identify a first TTI having a firstduration that comprises two or more symbol periods and a second TTIhaving a second duration that is less than the first duration asdescribed above with reference to FIGS. 2 through 10. In certainexamples, the operations of block 1505 may be performed by the TTIduration component as described with reference to FIGS. 12 and 13.

At block 1510, the UE 115 may identify a first search space formonitoring for first control information associated with the first TTIas described above with reference to FIGS. 2 through 10. In certainexamples, the operations of block 1510 may be performed by the searchspace component as described with reference to FIGS. 12 and 13.

At block 1515, the UE 115 may determine, based on the first searchspace, a second search space for monitoring for second controlinformation associated with the second TTI as described above withreference to FIGS. 2 through 10. In certain examples, the operations ofblock 1515 may be performed by the search space component as describedwith reference to FIGS. 12 and 13. The UE 115 may then monitor at leastone of the first search space for the first control information or thesecond for the second control information, as discussed above withrespect to FIGS. 2 through 10.

FIG. 16 shows a flowchart illustrating a method 1600 for control channelsignaling with multiple TTI lengths in accordance with various aspectsof the present disclosure. The operations of method 1600 may beimplemented by a device such as a UE 115 or its components as describedwith reference to FIGS. 1 and 2. For example, the operations of method1600 may be performed by the control information manager as describedherein. In some examples, the UE 115 may execute a set of codes tocontrol the functional elements of the device to perform the functionsdescribed below. Additionally or alternatively, the UE 115 may performaspects the functions described below using special- purpose hardware.

At block 1605, the UE 115 may identify a first TTI having a firstduration that comprises two or more symbol periods and a second TTIhaving a second duration that is less than the first duration asdescribed above with reference to FIGS. 2 through 10. In certainexamples, the operations of block 1605 may be performed by the TTIduration component as described with reference to FIGS. 12 and 13.

At block 1610, the UE 115 may identify a first search space formonitoring for first control information associated with the first TTIas described above with reference to FIGS. 2 through 10. In some cases,the identifying the first search space comprises: deriving a set ofdecoding candidates for decoding of received wireless transmissions andID of the first control information and the second control information.In certain examples, the operations of block 1610 may be performed bythe search space component as described with reference to FIGS. 12 and13.

At block 1615, the UE 115 may determine, based on the first searchspace, a second search space for monitoring for second controlinformation associated with the second TTI as described above withreference to FIGS. 2 through 10. In some cases, the determining thesecond search space comprises: identifying a second subset of thedecoding candidates as being in the second search space. In certainexamples, the operations of block 1615 may be performed by the searchspace component as described with reference to FIGS. 12 and 13.

At block 1620, the UE 115 may identify a first subset of the decodingcandidates as being in the first search space as described above withreference to FIGS. 2 through 10. In certain examples, the operations ofblock 1620 may be performed by the decoding candidate component asdescribed with reference to FIGS. 12 and 13.

FIG. 17 shows a flowchart illustrating a method 1700 for control channelsignaling with multiple TTI lengths in accordance with various aspectsof the present disclosure. The operations of method 1700 may beimplemented by a device such as a UE 115 or its components as describedwith reference to FIGS. 1 and 2. For example, the operations of method1700 may be performed by the control information manager as describedherein. In some examples, the UE 115 may execute a set of codes tocontrol the functional elements of the device to perform the functionsdescribed below. Additionally or alternatively, the UE 115 may performaspects the functions described below using special-purpose hardware.

At block 1705, the UE 115 may identify a first TTI having a firstduration that comprises two or more symbol periods and a second TTIhaving a second duration that is less than the first duration asdescribed above with reference to FIGS. 2 through 10. In certainexamples, the operations of block 1705 may be performed by the TTIduration component as described with reference to FIGS. 12 and 13.

At block 1710, the UE 115 may identify a first search space formonitoring for first control information associated with the first TTIas described above with reference to FIGS. 2 through 10. In certainexamples, the operations of block 1710 may be performed by the searchspace component as described with reference to FIGS. 12 and 13.

At block 1715, the UE 115 may determine, based on the first searchspace, a second search space for monitoring for second controlinformation associated with the second TTI as described above withreference to FIGS. 2 through 10. In certain examples, the operations ofblock 1715 may be performed by the search space component as describedwith reference to FIGS. 12 and 13.

At block 1720, the UE 115 may monitor the first search space and mayblind decode wireless transmissions received in the first search spacefor the first control information as described above with reference toFIGS. 2 through 10. In certain examples, the operations of block 1720may be performed by the decoder as described with reference to FIGS. 12and 13.

At block 1725, the UE 115 may monitor the second search space and mayblind decode wireless transmissions received in the second search spacefor the second control information as described above with reference toFIGS. 2 through 10. In certain examples, the operations of block 1725may be performed by the decoder as described with reference to FIGS. 12and 13.

FIG. 18 shows a flowchart illustrating a method 1800 for control channelsignaling with multiple TTI lengths in accordance with various aspectsof the present disclosure. The operations of method 1800 may beimplemented by a device such as a UE 115 or its components as describedwith reference to FIGS. 1 and 2. For example, the operations of method1800 may be performed by the control information manager as describedherein. In some examples, the UE 115 may execute a set of codes tocontrol the functional elements of the device to perform the functionsdescribed below. Additionally or alternatively, the UE 115 may performaspects the functions described below using special-purpose hardware.

At block 1805, the UE 115 may identify a first TTI having a firstduration that comprises two or more symbol periods and a second TTIhaving a second duration that is less than the first duration asdescribed above with reference to FIGS. 2 through 10. In certainexamples, the operations of block 1805 may be performed by the TTIduration component as described with reference to FIGS. 12 and 13.

At block 1810, the UE 115 may identify a first search space formonitoring for first control information associated with the first TTIas described above with reference to FIGS. 2 through 10. In certainexamples, the operations of block 1810 may be performed by the searchspace component as described with reference to FIGS. 12 and 13.

At block 1815, the UE 115 may determine, based on the first searchspace, a second search space for monitoring for second controlinformation associated with the second TTI as described above withreference to FIGS. 2 through 10. In certain examples, the operations ofblock 1815 may be performed by the search space component as describedwith reference to FIGS. 12 and 13.

At block 1820, the UE 115 may identify a first RTT for HARQ feedbackassociated with the first control information as described above withreference to FIGS. 2 through 10. In certain examples, the operations ofblock 1820 may be performed by the HARQ component as described withreference to FIGS. 12 and 13.

At block 1825, the UE 115 may identify a second RTT for HARQ feedbackassociated with the second control information, where the second RTT isshorter than the first RTT as described above with reference to FIGS. 2through 10. In certain examples, the operations of block 1825 may beperformed by the HARQ component as described with reference to FIGS. 12and 13.

FIG. 19 shows a flowchart illustrating a method 1900 for control channelsignaling with multiple TTI lengths in accordance with various aspectsof the present disclosure. The operations of method 1900 may beimplemented by a device such as a UE 115 or its components as describedwith reference to FIGS. 1 and 2. For example, the operations of method1900 may be performed by the control information manager as describedherein. In some examples, the UE 115 may execute a set of codes tocontrol the functional elements of the device to perform the functionsdescribed below. Additionally or alternatively, the UE 115 may performaspects the functions described below using special-purpose hardware.

At block 1905, the UE 115 may identify a first TTI having a firstduration that comprises two or more symbol periods and a second TTIhaving a second duration that is less than the first duration asdescribed above with reference to FIGS. 2 through 10. In certainexamples, the operations of block 1905 may be performed by the TTIduration component as described with reference to FIGS. 12 and 13.

At block 1910, the UE 115 may identify a first search space formonitoring for first control information associated with the first TTIas described above with reference to FIGS. 2 through 10. In certainexamples, the operations of block 1910 may be performed by the searchspace component as described with reference to FIGS. 12 and 13.

At block 1915, the UE 115 may determine, based on the first searchspace, a second search space for monitoring for second controlinformation associated with the second TTI as described above withreference to FIGS. 2 through 10. In certain examples, the operations ofblock 1915 may be performed by the search space component as describedwith reference to FIGS. 12 and 13.

At block 1920, the UE 115 may determine a third search space in thesecond slot for monitoring for the second subset of second controlinformation as described above with reference to FIGS. 2 through 10. Insome cases, the second control information comprises a first subset ofsecond control information transmitted in a first slot of a wirelesstransmission subframe and a second subset of second control informationtransmitted in a second slot of the wireless transmission subframe. Incertain examples, the operations of block 1920 may be performed by thesearch space component as described with reference to FIGS. 12 and 13.

At block 1925, the UE 115 may determine a starting symbol for the sharedchannel data transmissions in the second slot based on the third searchspace as described above with reference to FIGS. 2 through 10. Incertain examples, the operations of block 1925 may be performed by themultiplexing component as described with reference to FIGS. 12 and 13.

It should be noted that these methods describe possible implementation,and that the operations and the steps may be rearranged or otherwisemodified such that other implementations are possible. In some examples,aspects from two or more of the methods may be combined. For example,aspects of each of the methods may include steps or aspects of the othermethods, or other steps or techniques described herein. Thus, aspects ofthe disclosure may provide for control channel signaling with multipleTTI lengths.

The description herein is provided to enable a person skilled in the artto make or use the disclosure. Various modifications to the disclosurewill be readily apparent to those skilled in the art, and the genericprinciples defined herein may be applied to other variations withoutdeparting from the scope of the disclosure. Thus, the disclosure is notto be limited to the examples and designs described herein but is to beaccorded the broadest scope consistent with the principles and novelfeatures disclosed herein.

The functions described herein may be implemented in hardware, softwareexecuted by a processor, firmware, or any combination thereof. Ifimplemented in software executed by a processor, the functions may bestored on or transmitted over as one or more instructions or code on acomputer-readable medium. Other examples and implementations are withinthe scope of the disclosure and appended claims. For example, due to thenature of software, functions described above can be implemented usingsoftware executed by a processor, hardware, firmware, hardwiring, orcombinations of any of these. Features implementing functions may alsobe physically located at various positions, including being distributedsuch that portions of functions are implemented at different PHYlocations. Also, as used herein, including in the claims, “or” as usedin a list of items (for example, a list of items prefaced by a phrasesuch as “at least one of” or “one or more”) indicates an inclusive listsuch that, for example, a list of at least one of A, B, or C means A orB or C or AB or AC or BC or ABC (i.e., A and B and C).

Computer-readable media includes both non-transitory computer storagemedia and communication media including any medium that facilitatestransfer of a computer program from one place to another. Anon-transitory storage medium may be any available medium that can beaccessed by a general purpose or special purpose computer. By way ofexample, and not limitation, non-transitory computer-readable media cancomprise RAM, ROM, electrically erasable programmable read only memory(EEPROM), compact disk (CD) ROM or other optical disk storage, magneticdisk storage or other magnetic storage devices, or any othernon-transitory medium that can be used to carry or store desired programcode means in the form of instructions or data structures and that canbe accessed by a general-purpose or special-purpose computer, or ageneral-purpose or special-purpose processor. Also, any connection isproperly termed a computer-readable medium. For example, if the softwareis transmitted from a website, server, or other remote source using acoaxial cable, fiber optic cable, twisted pair, digital subscriber line(DSL), or wireless technologies such as infrared, radio, and microwave,then the coaxial cable, fiber optic cable, twisted pair, DSL, orwireless technologies such as infrared, radio, and microwave areincluded in the definition of medium. Disk and disc, as used herein,include CD, laser disc, optical disc, digital versatile disc (DVD),floppy disk and Blu-ray disc where disks usually reproduce datamagnetically, while discs reproduce data optically with lasers.Combinations of the above are also included within the scope ofcomputer-readable media.

Techniques described herein may be used for various wirelesscommunications systems such as CDMA, TDMA, FDMA, OFDMA, single carrierfrequency division multiple access (SC-FDMA), and other systems. Theterms “system” and “network” are often used interchangeably. A CDMAsystem may implement a radio technology such as CDMA2000, UniversalTerrestrial Radio Access (UTRA), etc. CDMA2000 covers IS-2000, IS-95,and IS-856 standards. IS-2000 Releases 0 and A are commonly referred toas CDMA2000 1X, 1X, etc. IS-856 (TIA-856) is commonly referred to asCDMA2000 1xEV-DO, High Rate Packet Data (HRPD), etc. UTRA includesWideband CDMA (WCDMA) and other variants of CDMA. A TDMA system mayimplement a radio technology such as (Global System for Mobilecommunications (GSM)). An OFDMA system may implement a radio technologysuch as Ultra Mobile Broadband (UMB), Evolved UTRA (E-UTRA), IEEE802.11, IEEE 802.16 (WiMAX), IEEE 802.20, Flash-OFDM, etc. UTRA andE-UTRA are part of Universal Mobile Telecommunications system (UniversalMobile Telecommunications System (UMTS)). 3GPP LTE and LTE-advanced(LTE-A) are new releases of UMTS that use E-UTRA. UTRA, E-UTRA, UMTS,LTE, LTE-a, and GSM are described in documents from an organizationnamed “3rd Generation Partnership Project” (3GPP). CDMA2000 and UMB aredescribed in documents from an organization named “3rd GenerationPartnership Project 2” (3GPP2). The techniques described herein may beused for the systems and radio technologies mentioned above as well asother systems and radio technologies. The description herein, however,describes an LTE system for purposes of example, and LTE terminology isused in much of the description above, although the techniques areapplicable beyond LTE applications.

In LTE/LTE-A networks, including networks described herein, the termevolved node B (eNB) may be generally used to describe the basestations. The wireless communications system or systems described hereinmay include a heterogeneous LTE/LTE-A network in which different typesof eNBs provide coverage for various geographical regions. For example,each eNB or base station may provide communication coverage for a macrocell, a small cell, or other types of cell. The term “cell” is a 3GPPterm that can be used to describe a base station, a carrier or componentcarrier (CC) associated with a base station, or a coverage area (e.g.,sector, etc.) of a carrier or base station, depending on context.

Base stations may include or may be referred to by those skilled in theart as a base transceiver station, a radio base station, an access point(AP), a radio transceiver, a NodeB, eNodeB (eNB), Home NodeB, a HomeeNodeB, or some other suitable terminology. The geographic coverage areafor a base station may be divided into sectors making up only a portionof the coverage area. The wireless communications system or systemsdescribed herein may include base stations of different types (e.g.,macro or small cell base stations). The UEs described herein may be ableto communicate with various types of base stations and network equipmentincluding macro eNBs, small cell eNBs, relay base stations, and thelike. There may be overlapping geographic coverage areas for differenttechnologies. In some cases, different coverage areas may be associatedwith different communication technologies. In some cases, the coveragearea for one communication technology may overlap with the coverage areaassociated with another technology. Different technologies may beassociated with the same base station, or with different base stations.

A macro cell generally covers a relatively large geographic area (e.g.,several kilometers in radius) and may allow unrestricted access by UEswith service subscriptions with the network provider. A small cell is alower-powered base stations, as compared with a macro cell, that mayoperate in the same or different (e.g., licensed, unlicensed, etc.)frequency bands as macro cells. Small cells may include pico cells,femto cells, and micro cells according to various examples. A pico cell,for example, may cover a small geographic area and may allowunrestricted access by UEs with service subscriptions with the networkprovider. A femto cell may also cover a small geographic area (e.g., ahome) and may provide restricted access by UEs having an associationwith the femto cell (e.g., UEs in a closed subscriber group (CSG), UEsfor users in the home, and the like). An eNB for a macro cell may bereferred to as a macro eNB. An eNB for a small cell may be referred toas a small cell eNB, a pico eNB, a femto eNB, or a home eNB. An eNB maysupport one or multiple (e.g., two, three, four, and the like) cells(e.g., CCs). A UE may be able to communicate with various types of basestations and network equipment including macro eNBs, small cell eNBs,relay base stations, and the like.

The wireless communications system or systems described herein maysupport synchronous or asynchronous operation. For synchronousoperation, the base stations may have similar frame timing, andtransmissions from different base stations may be approximately alignedin time. For asynchronous operation, the base stations may havedifferent frame timing, and transmissions from different base stationsmay not be aligned in time. The techniques described herein may be usedfor either synchronous or asynchronous operations.

The DL transmissions described herein may also be called forward linktransmissions while the UL transmissions may also be called reverse linktransmissions. Each communication link described herein including, forexample, wireless communications system 100 and 200 of FIGS. 1 and 2 mayinclude one or more carriers, where each carrier may be a signal made upof multiple sub-carriers (e.g., waveform signals of differentfrequencies). Each modulated signal may be sent on a differentsub-carrier and may carry control information (e.g., reference signals,control channels, etc.), overhead information, user data, etc. Thecommunication links described herein (e.g., communication links 125 ofFIG. 1) may transmit bidirectional communications using frequencydivision duplex (FDD) (e.g., using paired spectrum resources) or TDDoperation (e.g., using unpaired spectrum resources). Frame structuresmay be defined for FDD (e.g., frame structure type 1) and TDD (e.g.,frame structure type 2).

Thus, aspects of the disclosure may provide for control channelsignaling with multiple TTI lengths. It should be noted that thesemethods describe possible implementations, and that the operations andthe steps may be rearranged or otherwise modified such that otherimplementations are possible. In some examples, aspects from two or moreof the methods may be combined.

The various illustrative blocks and modules described in connection withthe disclosure herein may be implemented or performed with ageneral-purpose processor, a digital signal processor (DSP), an ASIC, anfield programmable gate array (FPGA) or other programmable logic device,discrete gate or transistor logic, discrete hardware components, or anycombination thereof designed to perform the functions described herein.A general-purpose processor may be a microprocessor, but in thealternative, the processor may be any conventional processor,controller, microcontroller, or state machine. A processor may also beimplemented as a combination of computing devices (e.g., a combinationof a DSP and a microprocessor, multiple microprocessors, one or moremicroprocessors in conjunction with a DSP core, or any other suchconfiguration). Thus, the functions described herein may be performed byone or more other processing units (or cores), on at least oneintegrated circuit (IC). In various examples, different types of ICs maybe used (e.g., Structured/Platform ASICs, an FPGA, or anothersemi-custom IC), which may be programmed in any manner known in the art.The functions of each unit may also be implemented, in whole or in part,with instructions embodied in a memory, formatted to be executed by oneor more general or application-specific processors.

All structural and functional equivalents to the elements of the variousaspects described throughout this disclosure that are known or latercome to be known to those of ordinary skill in the art are expresslyincorporated herein by reference and are intended to be encompassed bythe claims. Moreover, nothing disclosed herein is intended to bededicated to the public regardless of whether such disclosure isexplicitly recited in the claims. The words “module,” “mechanism,”“element,” “device,” “component,” and the like may not be a substitutefor the word “means.” As such, no claim element is to be construed as ameans plus function unless the element is expressly recited using thephrase “means for.”

What is claimed is:
 1. A method of wireless communication comprising:identifying a first transmission time interval (TTI) with a firstduration that includes two or more symbol periods and a second TTI witha second duration that is less than the first duration; identifying afirst search space for monitoring for first control informationassociated with the first TTI; determining, based at least in part onthe first search space, a second search space for monitoring for secondcontrol information associated with the second TTI; and monitoring atleast one of the first search space for the first control information orthe second for the second control information.
 2. The method of claim 1,wherein the second search space is correlated to the first search space.3. The method of claim 1, wherein the second search space is a subset ofthe first search space.
 4. The method of claim 1, wherein theidentifying the first search space comprises: deriving a plurality ofdecoding candidates for decoding of received wireless transmissions andidentification of the first control information and the second controlinformation; and identifying a first subset of the decoding candidatesas being in the first search space.
 5. The method of claim 4, whereinthe determining the second search space comprises: identifying a secondsubset of the decoding candidates as being in the second search space.6. The method of claim 5, wherein the first subset of decodingcandidates and the second subset of decoding candidates arenon-overlapping subsets of the plurality of decoding candidates.
 7. Themethod of claim 4, wherein the deriving is based at least in part on oneor more of a user equipment (UE) network identifier, a random seed, or atotal size available for control information.
 8. The method of claim 7,wherein the determining the second search space comprises: deriving thesecond search space based at least in part on one or more of a second UEnetwork identifier or a second random seed.
 9. The method of claim 1,wherein the first control information comprises first downlink controlinformation (DCI) having a first DCI size and a first DCI format, andthe second control information comprises second DCI having a second DCIsize and a second DCI format, and wherein one or more of the first DCIsize and the second DCI size or the first DCI format and the second DCIformat is different.
 10. The method of claim 9, wherein the first DCIsize is larger than the second DCI size.
 11. The method of claim 9,wherein the first DCI size and second DCI size are the same, and whereinone or more bits of the second DCI provide different information thancorresponding bits in the first DCI.
 12. The method of claim 9, whereinthe first DCI includes a first number of cyclic redundancy check (CRC)bits, and the second DCI includes a second number of CRC bits that isgreater than the first number of CRC bits.
 13. The method of claim 1,wherein the monitoring comprises: blind decoding wireless transmissionsreceived in the first search space for the first control information;and blind decoding wireless transmissions received in the second searchspace for the second control information.
 14. The method of claim 13,further comprising: identifying a set of blind decoding candidates forblind decoding transmissions received in the second search space basedat least in part on one or more of an available number of aggregationlevels for second TTI transmissions or an available DCI format for thesecond control information.
 15. The method of claim 14, wherein adifferent set of blind decoding candidates for the first search space isidentified when transmissions using the second TTI are configured thanwhen transmissions using the second TTI are not configured.
 16. Themethod of claim 13, further comprising: identifying a set of blinddecoding candidates for blind decoding transmissions received in thesecond search space based at least in part on a round trip time (RTT)for hybrid automatic repeat request (HARQ) feedback associated with thesecond control information.
 17. The method of claim 1, furthercomprising: identifying a first RTT for HARQ feedback associated withthe first control information; and identifying a second RTT for HARQfeedback associated with the second control information, wherein thesecond RTT is shorter than the first RTT.
 18. The method of claim 17,wherein the second RTT is determined based at least in part on acapability of a UE receiving the second control information.
 19. Themethod of claim 18, wherein the first RTT is determined to be a legacyRTT or a shorter RTT than the legacy RTT based at least in part on thecapability of the UE.
 20. The method of claim 1, wherein the secondcontrol information comprises a first subset of second controlinformation transmitted in a first slot of a wireless transmissionsubframe and a second subset of second control information transmittedin a second slot of the wireless transmission subframe.
 21. The methodof claim 20, wherein the first subset transmitted in the first slot ofthe wireless transmission subframe is transmitted in a control channelthat is time division multiplexed with shared channel data transmissionsin the first slot, and wherein second subset transmitted in the secondslot of the wireless transmission subframe is transmitted in a secondcontrol channel that is both time division multiplexed and frequencydivision multiplexed with shared channel data transmissions in thesecond slot.
 22. The method of claim 20, further comprising: determininga starting symbol for the shared channel data transmissions in thesecond slot based at least in part on one or more of a configuredstarting symbol location or a symbol location of the second subset ofsecond control information.
 23. The method of claim 20, furthercomprising: determining a third search space in the second slot formonitoring for the second subset of second control information; anddetermining a starting symbol for the shared channel data transmissionsin the second slot based at least in part on the third search space. 24.The method of claim 23, wherein the third search space is determinedbased at least in part on a set of resource blocks (RBs) of the secondslot configured for control information transmissions.
 25. The method ofclaim 23, wherein the first search space and second search space aredistributed over a system bandwidth for transmissions in the first slot,and wherein the third search space is distributed over a subset of thesystem bandwidth.
 26. The method of claim 23, wherein the third searchspace is determined based at least in part on a transmission modeassociated with the second control information.
 27. The method of claim20, wherein the second subset of second control information comprisesone or more of physical downlink control channel (PDCCH) information orphysical control format indicator channel (PCFICH) informationtransmitted in the second slot of the wireless transmission subframe.28. An apparatus for wireless communication comprising: means foridentifying a first transmission time interval (TTI) with a firstduration that includes two or more symbol periods and a second TTI witha second duration that is less than the first duration; means foridentifying a first search space for monitoring for first controlinformation associated with the first TTI; means for determining, basedat least in part on the first search space, a second search space formonitoring for second control information associated with the secondTTI; and means for monitoring at least one of the first search space forthe first control information or the second for the second controlinformation.
 29. An apparatus for wireless communication, comprising: aprocessor; memory in electronic communication with the processor; andinstructions stored in the memory and operable, when executed by theprocessor, to cause the apparatus to: identify a first transmission timeinterval (TTI) with a first duration that includes two or more symbolperiods and a second TTI with a second duration that is less than thefirst duration; identify a first search space for monitoring for firstcontrol information associated with the first TTI; determine, based atleast in part on the first search space, a second search space formonitoring for second control information associated with the secondTTI; and monitor at least one of the first search space for the firstcontrol information or the second for the second control information.30. A non-transitory computer-readable medium storing code for wirelesscommunication, the code comprising instructions executable to: identifya first transmission time interval (TTI) with a first duration thatincludes two or more symbol periods and a second TTI with a secondduration that is less than the first duration; identify a first searchspace for monitoring for first control information associated with thefirst TTI; determine, based at least in part on the first search space,a second search space for monitoring for second control informationassociated with the second TTI; and monitor at least one of the firstsearch space for the first control information or the second for thesecond control information.